Warships and aircraft from five nations operated together inside the Philippines’ exclusive economic zone on September 28, 2024, in a coordinated show of military cooperation that directly challenges Beijing’s expansive maritime claims in the South China Sea. Australia, Japan, New Zealand, the Philippines, and the United States participated in what officials labeled a Maritime Cooperative Activity, with Australia contributing the guided-missile destroyer HMAS Sydney and a Royal Australian Air Force P-8A Poseidon maritime patrol aircraft. The exercise followed a similar four-nation operation in April 2024 and signals an accelerating pattern of joint military activity in waters where Chinese coast guard and naval vessels have repeatedly confronted Philippine ships.
Why five-nation patrols inside the Philippine EEZ raise the cost of Chinese pushback
The September 28 activity was not a routine bilateral drill. By bringing together forces from five countries inside the Philippine exclusive economic zone, the participating governments turned what could have been a quiet training event into a public statement about who has the right to operate in those waters. The Australian release explicitly stated that the activity took place within the Philippines’ EEZ and described it as consistent with international law. That framing matters because China claims historic rights over much of the South China Sea, including areas that overlap with the Philippine EEZ, and has used coast guard vessels and water cannons to block Philippine resupply missions near contested features.
The logic behind these publicized transits is straightforward. Each time a group of allied and partner navies sails through the Philippine EEZ together, any Chinese interference would create a diplomatic incident involving not just Manila but also Washington, Tokyo, Canberra, and Wellington. That raises the political price Beijing would pay for aggressive action without activating the formal mutual defense treaty between the United States and the Philippines, which applies only to armed attacks on Philippine forces, vessels, or aircraft in the Pacific. The five participating nations can demonstrate solidarity and complicate Chinese decision-making while keeping the encounter below the threshold of a treaty-triggering event.
This calibrated approach also serves a domestic audience in each capital. For Manila, the presence of allied warships reinforces the message that the Philippines is not alone in defending its maritime rights. For Washington and Tokyo, the operations show taxpayers and lawmakers that security partnerships in the Indo-Pacific produce visible, coordinated action rather than abstract commitments. For Australia and New Zealand, participation underscores their roles as regional security contributors and reinforces their stated support for a rules-based order at sea.
Official records trace a pattern from April to September 2024
Two primary government documents establish the factual record for these operations. The first is the Australian Defence Department’s release confirming the September 28 Maritime Cooperative Activity. That document named all five participating countries, identified HMAS Sydney and the RAAF P-8A as Australian contributions, and stated the exercise occurred within the Philippine EEZ. The release also affirmed that the activity was consistent with international law, a phrase that implicitly invokes the United Nations Convention on the Law of the Sea and the 2016 arbitral tribunal ruling that rejected China’s sweeping South China Sea claims.
The second key document is the joint statement from the Philippines-United States Fourth 2+2 Ministerial Dialogue, which praised an April activity involving the Philippines, the United States, Japan, and Australia. That earlier operation also took place in the Philippines’ exclusive economic zone. The joint statement connected the April activity to broader goals of improving interoperability among the four forces and upholding international law, including UNCLOS, signaling that such patrols are part of a long-term strategy rather than ad hoc responses.
Taken together, the two documents show that the September operation was not a one-off event but a deliberate expansion of an established format. The April drill involved four nations. Five months later, New Zealand joined, widening the coalition. The progression suggests that participating governments view these activities as a repeatable tool for signaling collective resolve in the South China Sea, with room to add partners over time while retaining a Philippine lead role inside its own EEZ.
The pattern also highlights a division of labor. The Philippines provides the legal and geographic anchor by hosting activities within its EEZ, while treaty allies and close partners contribute high-end assets such as destroyers, maritime patrol aircraft, and potentially submarines or surveillance platforms. This mix allows Manila to showcase international backing without having to match Chinese naval capacity on its own.
Gaps in the operational record and what to watch next
Several questions remain unanswered by the available official records. No primary Japanese government statement about the September 28 activity has surfaced, leaving the specific Japanese naval assets involved unconfirmed. The Australian release listed only Australian contributions, and the U.S.-Philippines joint statement addressed the April operation rather than the September one. That means the full order of battle for the five-nation exercise, including which ships Japan, New Zealand, the Philippines, and the United States deployed, is not documented in publicly available primary sources.
Exact geographic coordinates, the duration of the activity, and the specific maneuvers conducted inside the EEZ are also absent from the official releases. Neither document describes any Chinese military or coast guard response to the operations. Without that information, it is difficult to assess whether Beijing chose to shadow, challenge, or ignore the transit, or whether any radio warnings or close approaches occurred. Direct statements from Philippine or Japanese commanders about rules of engagement or observed Chinese behavior have not appeared in the public record.
Those gaps limit outside analysts’ ability to judge the operational risk the participants accepted. A patrol that stays far from Chinese-occupied features and avoids contested shoals carries a different escalation profile than one that passes directly by areas where collisions and water-cannon incidents have occurred. Without coordinates or detailed after-action reports, it is only possible to say that the activity took place somewhere within the broad expanse of the Philippine EEZ, which covers large swaths of the eastern and central South China Sea.
The next development to watch is whether the coalition expands again. New Zealand’s addition in September suggests that the format is designed to accommodate new participants over time. South Korea, Canada, and European navies such as France and the United Kingdom have all conducted their own South China Sea transits in recent years, and any of them could join a future Maritime Cooperative Activity. A larger coalition would further raise the diplomatic cost of Chinese interference but would also require more complex planning, communications, and deconfliction among a wider set of navies.
Another variable is frequency. If these operations remain occasional, they will function mainly as symbolic demonstrations of unity. If they become quarterly or even more regular, they could normalize the presence of multinational patrols inside the Philippine EEZ and gradually shift expectations about who routinely operates there. That, in turn, could influence how regional states and outside powers interpret the balance of power and the credibility of international law in the South China Sea.
For now, the September 28 patrol underscores that the April operation was the start of a series, not a one-time gesture. With limited but clear official documentation, the record shows a growing network of partners willing to be physically present in contested waters under Philippine lead. How often they return, who joins next, and how China chooses to respond will determine whether these Maritime Cooperative Activities remain low-key exercises or evolve into a central feature of the region’s emerging security architecture.
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*This article was researched with the help of AI, with human editors creating the final content.
